Summary

Flight 2-45-81 was flown by Lt. Col. Robert A. Rushworth on July 1, 1966, to (a) obtain handling qualities data with full external tanks installed and at M = 6, (b) evaluate external tank separation characteristics, (c) evaluation of ablatives located on lower vertical stabilizer, jettisonable ventral, nose gear door, and "hard points", (d) obtain data on local flow conditions in the proposed ramjet location, (e) to evaluate the alternate pitot-static system, and (f) obtain base pressure data.

The objectives of the flight were not accomplished as planned, however, the prime objective, i.e., to obtain flight characteristics with the full external tanks installed on the X-15, was accomplished. The planned flight was terminated early after telemetry signals indicated ammonia was not feeding from the external tank. The external tanks were jettisoned and a planned alternate landing was made on Mud Lake, Nevada.

The pilot considered the handling qualities with full tanks on, to have been adequately predicted by the simulator and acceptable. The handling qualities of the aircraft with full tanks were reported to be not significantly different than with empty tanks.

The pilot ejected the external tanks using the button which activates the system designated for full propellant tanks. Tank separation was nearly simultaneous with the NH3 tank leading. The external tanks separated cleanly from the X-15 as had been the case with the empty tanks. Both tanks were recovered in repairable condition.

Data for evaluation of the ablative material was not acquired during this flight. Some data were obtained as planned for local flow measurement at the lower ventral. Initial data review indicates that static pressure data were not obtained at the lower ventral area. Data were obtained on the alternate pitot-static system and the system functioned satisfactorily.

Flight Profile

The planned flight, to evaluate the aircraft handling qualities with full external tanks installed, was terminated approximately 18 seconds after launch because of an indication that propellant was not feeding from the external ammonia tank. The pilot ejected the external tanks and made a successful landing at Mud Lake, Nevada as shown in figure 1. The airplane arrived at Mud Lake with significantly more energy than had been expected.

The launch was considered to be less severe than normal X-15 launches. After launch the aircraft rolled 10 degrees to the right accompanied by a 1 1/2 degrees nose left sideslip. Approximately 1.4 seconds after launch, the pilot ignited the engine while at 4 degrees angle of attack and continued to increase the angle of attack to 8 degrees. The pilot then advanced the throttle to 100% thrust and observed the expected nose down trim change (angle of attack dropped to 4°) because the center of gravity is below the centerline of the aircraft. The pilot increased to the planned rotation angle of attack of 12 degrees with occasional overshoots to 14 degrees.

The internal recordings indicate a lateral control deflection was used to maintain wings level. The roll horizontal stabilizer deflection averaged about 4 degrees during the first 6 to 8 seconds after launch, reaching a peak of 6 degrees. These values are very close to those which had been predicted. The pilot however was not aware of using lateral control.

Approximately 18 seconds after the engine light, the pilot received the call from NASA 1, that "no flow" was observed from the external ammonia tank. The pilot immediately started a pushover to zero degrees angle of attack and at 20.9 seconds reduced to minimum thrust. The external tanks were ejected with the full button 28 seconds after engine light, at approximately M » 1.4, at a dynamic pressure of about 620 PSF. The angle of attack at tank drop was about 6 degrees and the normal acceleration was about 1.2 "g".

The engine was shutdown 33.2 seconds after the engine light and the maximum velocity was about 1500 FPS. The pilot started a turn to Mud Lake while jettisoning internal propellants. The landing was made on Mud Lake without incident.

Tank Ejection

The decision to eject the external tank prematurely was based on a failure to receive the telemetered flow signal for the pressurizing gas (helium) in the external NH3 tank. The ground rule to take action upon this measurement was established prior to flight and "proven" to be a valid method during preflight operations which included an engine run and a captive flight. This quantity was not presented to the pilot but rather telemetered to NASA 1. A check of this parameter was satisfactory during the prelaunch jettison check and engine operation. However, it did not respond adequately after launch and therefore, the pilot was advised to abort the planned mission. Postflight analysis has since concluded that normal flow did exist from the external NH3 tank. This is based on the fact that (1) the internal NH3 Fox source did not start to decrease until after the pilot selected "internal" feed just prior to tank ejection, (2) postflight analysis proved the pressure transducer from the NH3 tank to inoperative, (3) the internal propellant jettison was normal (NH3 - 118 sec, LOX - 107 sec) (4) no abnormal handling characteristics existed as would have been the case because of abnormal c.g. locations. It has been agreed by all concerned that the pilot must be presented this critical parameter in the future. Consideration should also be given to making the information source redundant.

Ejection of the tanks by the "Full" button was designed to initiate only 2 of the 4 ejector cartridges (1/2 force) and not to fire the separation rocket. However, in this case, apparently because of faulty circuitry, the separation rocket did fire. The separation occurred without the tanks recontacting the aircraft even in the off design conditions of high q with partially loaded external tanks having an adverse aft center of gravity. However, inspection of the ejector bearing points on the aircraft indicate that the NH3 tank was in some manner displaced in that the ejector rods marred the bearing points in an off center manner.

The tank recovery system worked satisfactorily in that both tanks were recovered intact. The drogue chutes deployed immediately after separation and the dump valve in the tank allowed the propellants to dump.

The gyrating, tumbling motion of the tanks while on the drogue chute (observed also on the empty tank drop) was present during this drop. Main chute deployment was satisfactory; however, the mechanism designed to cut the main chute risers, as the tanks touch down failed and the tanks were dragged over large distances because of high surface winds. Both tanks were recovered in repairable condition.

The reaction of the X-15 to the ejection of partially filled tanks was of a greater magnitude than for the empty tank ejection of flight 2-43. Figure 2 presents a comparison between the two tank ejections. At tank ejection an initial left roll of 34 deg/sec was induced followed by a roll to the right of 45 deg/sec. These motions resulted in sufficient SAS inputs to drive the right SAS servo hard over for a short period thereby decreasing the amount of damping available and allowing the oscillation to persist over a longer time period. The two distinct increases in normal acceleration as angle of attack is decreasing, along with similar trends in transverse and longitudinal accelerations tend to indicate that the right (NH3) separated before separation of the LOX tank. The telemetered external tank pressures terminate within 0.06 seconds of each other, indicating that the tanks must have separated almost simultaneously. Further analysis of the tank drop trim changes are in progress.

Handling Qualities

The pilot reported that the launch from the B-52 was less severe than normal launches. He reported the aircraft dropped farther than normal before he ignited the engine. He indicated there was not much difference between the tanks empty and full configurations at launch. The aircraft handling qualities were as good or better than observed on the simulator where handling qualities were considered acceptable. The pilot rated the launch and constant angle of attack portion of the flight as:

a f y

2.0 1.5 1.5

These handling qualities are somewhat better ratings than obtained with the empty tanks and are satisfactory.

The pilot indicated the simulator did not exactly duplicate the tank ejection. In particular, he felt the damping of the aircraft after tank ejection was somewhat less than shown on the simulator. He rated the tank drop as:

a f y

4.5 2.0 1.5

The pilot had rated the empty tank ejection as 2.5 in pitch. He indicated the tank drop was sharper in pitch and roll than experienced with the empty tanks, however, the handling qualities were acceptable.

Alternate Pitot-Static System

During the approach to the Mud Lake landing, the pilot actuated the alternate pitot-static system and compared the indicated airspeed of the extendible system with the standard ships system. The comparison between the two systems was excellent and the pilot considered the alternate system acceptable for flight. A detailed comparison is being made.

Martin Ablative Tests

Data were not obtained on the ablative material during this flight because the flight was terminated far short of the required flight conditions. The ablative material on the jettisonable ventral was scarred as the ventral was apparently dragged by the parachute following impact on the ground. The "hard points" did not appear to have been damaged from the external tank jettison. The ablative configuration will be flown again on the next flight.
 
 

Maurer Camera

The Maurer Camera was not flown as planned. Installation of the camera could not be accomplished as scheduled.

Ramjet Local Flow Conditions

Some data on local flow were obtained as planned. Initial checks of the tape playback indicate the static pressure did not record as expected. Further analysis of this problem is being conducted.

Canopy Hook Loads

Canopy hook loads were not obtained due to damage to the instrumentation when the canopy was closed for the ground engine runs. Methods of protecting the instrumentation are being considered.

B-52/X-15 Considerations

The B-52 pilot stated that no problem existed with the B-52 flight characteristics with this X-15 configuration other than a small degradation in performance. The B-52 pilot reported that the transient resulting from the X-15 launch was less than expected.

Instrumentation Discrepancies

Film drum speeds were erratic on oscillographs 0-18-36C, 0-26-36C and 0-l9-36C .

Temperature effects eliminated T/C data on oscillograph 0-9-36C.

Incorrect calibrate deflections were detected on:

Elmor J. Adkins, Head

X-15 Research Project Office